The present invention relates generally to the manufacture of extruded tubes and, more particularly, concerns an apparatus and method for handling freshly extruded tubes in order to avoid damaging them or distorting their shape.
Optical fiber is produced by drawing a glass structure known as a xe2x80x9cpreform.xe2x80x9d The preform may include a substrate tube and an over cladding tube, which need to have a precise size and shape in order to assure the quality of the ultimate fiber. These tubes have typically been manufactured by high-temperature deposition, drill, and draw or by a casting process, but such processes are relatively slow and the latter requires the simultaneous casting in hundreds of molds to produce a sufficient quantity of tubes to make the process commercially feasible.
It would therefore be desirable to manufacture these silica tubes by an extrusion process which would be relatively continuous and, therefore, faster and more efficient than the casting process.
The extrusion process, however, introduces its own complications. The relatively thin-walled tubes (about 40 millimeters in diameter with a wall thickness of about 5 millimeters) are extruded to a length of about 6 feet in order for the process to be practical, and are in a relatively soft state when first extruded. Moreover, the tubes must be handled extremely carefully in order to avoid damaging their surface or distorting their shape. In particular, the tube must not only be supported as it leaves the extruder, but must be supported on a moving surface which draws it away from the nozzle of the extruder. This is necessary in order to assure that the tube exiting by the extruder does not stick to the supporting surface and thereby become distorted or damage. Ceramic extruded tubes have been handled on inclined conveyor belts, but the silica tubing is too delicate and must meet far too stringent structural requirements to be subjected to such treatment. In addition, it is then necessary for each extruded length of tube to be supported and protected while it is carried away to a dryer. In the dryer, the tubes are typically supported on rotating rollers and dried for one or two days. The rotating rollers not only assure uniform drying, but guarantee that flat spots are not formed in the tubing.
In accordance with the present invention, a tube take-up apparatus is provided to handle a length of extruded tube. The apparatus includes an elongated housing which is removably securable to the extruder nozzle at a near end and extends away from it. A pair of parallel, spaced-apart rollers of a diameter approximately equal to the diameter of the extruded tubing extend along the length of the housing in a position just below the extruded tubing. The housing is removably mounted on an elongated supporting fin which is secured to the extruder at its near end and extends upwardly between the two rollers and substantially along the entire length of the housing. The supporting fin is, in turn, mounted on a fixed supporting base at its remote end. In operation, a fin ribbon made of a non-stick material, such as teflon, is supported on the upper edge of the supporting fin, and the tube is deposited on top of the ribbon as it is extruded. Simultaneously, the ribbon is drawn away from the extruding nozzle, so as to assist in drawing the extruded tube away from the nozzle and to prevent it from scraping along the supporting surface. The housing is dimensioned so that a full length of extruded tubing will fit in it. After the full length has been extruded, the housing and rollers as a unit are lifted from the supporting fin and are carried away as a unit to a dryer, with the extruded tube supported on the two rollers. Preferably, the axles of the rollers extend from the remote end of the housing and are adapted to be coupled to a motor which will drive them into rotation. The tube may therefore be dried directly within the housing, without any additional handling. In order to accommodate the next extruded tube, another housing/roller assembly is mounted on the supporting fin as the original one is removed, and the next tube is extruded.